DE1078624B - Pilot-controlled level control for an electrical communication system - Google Patents

Description

GERMAN

The invention relates to a pilot-controlled level control to compensate for the changes in attenuation on the lines of an electrical communication system, in particular a carrier frequency system, in which the level is regulated by means of an attenuator or an amplifier will. There are known arrangements, the proportionally operating controller (P controller) or integrating Use controller (I controller); An NTC thermistor is usually used as the actuator.

In the case of the P controller, there is a proportional relationship between the control deviation and the manipulated variable, i.e. in the present case between the deviation of the pilot voltage from the setpoint and the heating current for the NTC thermistor. The requirement for a small residual error, which always persists with this controller, makes a large control gain necessary. Then, however, all time constants that occur in the control loop in addition to the thermal time constant of the thermistor must be kept small in order to obtain satisfactory dynamics of the control process - which is synonymous with a low "modulation gain". Modulation amplification is understood to mean that, for certain frequencies of the level fluctuations, these fluctuations are amplified by the level control; This is particularly annoying when there are many controlled amplifiers in a chain on one control technology. Of disadvantage is also that the \ ^r erstärkung can not be held at the last the adjusted value at a P controller ³ at failure of the pilot voltage.

An integrating controller generally contains a motor which, according to the control deviation is driven and the heating current of the thermistor via a gear and an adjustable resistor changes. The motor-gear arrangement brings with it its own time constant for the controller, the due to the modulation gain sufficiently large compared to the thermal thermistor time constant have to be. This results in a relatively large control time constant, so that a line with Many such controllers in a chain only return to an undesirably long time after a level jump Calm comes. If the pilot voltage fails, the last motor from the controller can be switched off by stopping the motor set state can be retained.

The invention is based on the object of improving the known arrangements. In particular is required: Small modulation gain, not Control duration too long, small residual error in the steady state and retention of the manipulated variable in the event of failure Pilot voltage.

In the case of pilot-controlled level control, on which pilot-controlled level control is based

for an electric
Messaging system

Applicant:

Siemens & Halske Aktiengesellschaft,

Berlin and Munich,
Munich 2, Witteisbacherplatz 2

Dr.-Ing. Johann-Gerhard Zirwas, Munich,
has been named as the inventor

the invention relates, the level by means of a Attenuator or amplifier regulated; it contains a pilot voltage receiving and rectifying pilot receiver and a downstream DC amplifier acting on an actuator. The level control according to the invention is characterized in that an equivalent voltage regulated by a motor in the sense that it is equal to the output voltage of the DC amplifier is that the motor is fed by the difference between the two voltages and that the direct current amplifier is additionally supplied with a feedback direct current that corresponds to this voltage difference is proportional.

It is particularly advantageous that the backup voltage can be used in the event of a pilot failure. to maintain the regulated state.

A difference between the output voltage of the DC amplifier and the equivalent voltage occurs only temporarily during the control process. Because the voltage difference is used as a feedback variable is, the feedback is yielding, and the controller receives the behavior of a PI controller that the stability of the control loop is significantly improved.

In the exemplary embodiment, a thermistor is used as the actuator. The thermistor demands one like that large time constant for the feedback that it is not satisfactory with purely electrical components can be realized. By using an elec-

909 768/291

3 4

Electromechanical feedback by means of a motor and gear. This can be kept smaller, the larger

drives can be made by choosing the gear ratio that makes the gain μ. You are through, however

The time constant is precisely defined and the demands on the dynamics of the control process are based on this

Head of appropriate size -be brought. Narrow limits drawn by * · at "the known arrangement.

Adjustment of the feedback current can be the 5 If the input level pg small periodic

make the time constant as small as the permissible fluctuations show, the output

Modulation gain and the properties of the level p _{A make} fluctuations of the same frequency.

Allow thermistor. Regardless of this, the frequency of fluctuations can be very low

Residual errors due to a correspondingly high control gain, their amplitude is reduced by the control. at

can be kept small. io very high frequencies of the level fluctuation

The invention is described below on the basis of the controller (in particular because of the activity of the

Figure explained in more detail using an exemplary embodiment. Thermistor) no longer follow, and the amplitude

The control loop consists of a line gain fluctuation is passed on unchanged. In

ker V, a pilot receiver PE and the actual an intermediate area, there are frequencies at which

Regulator, which is essentially a direct current 15 the regulator via the inert thermistor as well as through

stronger M as well as a motor Z, which via the other time constants in the control loop (in particular

a transmission ü a potentiometer P adjusted. As a result of the indirect heating) so delayed

DC amplifier is in the embodiment, the gain acts that the original

a magnetic amplifier used. Fluctuations in the input level in the output

The line amplifier V is even appear amplified in the long-distance line 20 level. This »modulation of a carrier frequency system switched on. The gain should be kept smaller, the more are connected in a chain by the same control loops in the preceding line section.
Attenuation of the line to the low reception voltage. According to the invention, a level Pe voltage which has dropped to the transmission level p _A substitute voltage U _n is set by the motor Z in such a way that it amplifies with the am. It is the task of the controller, e.g. B. over 25 heaters of the thermistor lying voltage U _n agrees above one in the negative feedback path of the amplifier V lie-. The sensitive motor Z is on the low thermistor HL (actuator), for a voltage difference Δ U between U _H and U _H '. He agreed to ensure a constant output level p _A , adjusted via the transmission ü the potentiometer P in even if the input level p _E is in a certain sense that the voltage difference disappears. Borders changes. For this purpose, the pilot oscillation transmitted by the changeover line is short-circuited in the pilot contact a _{2 of} the ^ 4 relay and keeps the receiver PE sieved, amplified and rectified- potentiometer in the last set position . The output direct current I _P des obtained in this way is fixed. In addition, the changeover contact a ₂ pilot receiver is a measure of the controlled variable, namely the heater of the thermistor to the equivalent voltage U _n borrowed the output level p _{A of} the line amplifier. 35 placed so that the amplification of the line voltage Ip flows through the monitoring relay A amplifier V no longer changes. The presence and the control winding W _P of the magnetic amplifier M. The pilot voltage, the equivalent voltage U is _N With this still bears the two further Steuerwicklun- a resistor R ₂ loaded equal to the Widergen W _R and Ws and the load winding W _L. Each stand of the heater's thermistor is.
Winding consists of two identical partial windings, 40 With a simple P-controller it would be - as they are already applied to two separate iron cores. mentioned - a retention of the manipulated variable in the event of failure. Through the winding W _R flows in the steady state, the pilot voltage is not possible; at best, the regulated state could be no electricity, as will be shown. The winding W _s carries a direct current I ₀ , which can be switched with the mean value of the heating current, its constant flow to the current I _P in the 45 which, however, generally with the winding W _{P that was adjusted last} counteracts and the value does not match in the control loop. This would, however, define a certain setpoint value Jp ₀ . The output current I _{n of} the marer operation on the line in the event of a pilot failure not gneteamplifier is then more possible due to the deviation χ.

of the current I _P controlled by the setpoint Ip _0. If the input of the control amplifier is fed back

the amplification of the magnetic amplifier with μ denotes the 50 reference variable supplied to the voltage difference AU

If the polarity is correct, the control is proportional. The controller thus receives a subsequent

feedback that gives him a PI (proportional

1 = 1 — η. · Χ (1) tional-integral-) controller makes and the dynamic

⁰ Behavior with regard to the modulation gain

As long as the pilot level and thus the current I _P 55 improves significantly. The im

does not fall below a predetermined minimum value, the embodiment of the current I _R , which is determined by the

the armature of the relay A remains attracted and the control winding W _{K of} the magnetic amplifier M flows.

Current I _n flows through the changeover contact G ₁ through it is proportional to the voltage difference Δ U and

the heater of the indirectly heated thermistor HL in the steady, regulated state is equal to zero,

in the negative feedback path of amplifier V. Here is 60 The speed η of the motor is proportional to

the circuit of the amplifier is chosen so that with applied voltage Δ U. Then results for the

increasing heating current I _n the gain increases; time course of the voltage difference Δ U and

otherwise you have to z. B. the polarity of the winding thus also for the feedback variable:
Reverse W _P.

As far as described so far, it is about 65 "Ά U ₌ Ol. AU (2)

known arrangement of a proportionally acting fä ü

Control loop. Be a characteristic property.
it says that to change the heating current I _n

in the control area Δ I _n a certain residual error Δ χ --T (i \

the controlled variable according to equation (1) accept 70 Δ U (t) = Δ U (t = 0) · e ^u . W.

The frequency response F _r (p) of the feedback is thus:

PT ₇ .

with p = j

(4)

The time constant T ₁ . = - can be changed by a corresponding translation ü of the gearbox. The factor α is determined by the resistance R ₁ .

The improving effect of a yielding feedback on the dynamic behavior of a control loop is known and can be represented as follows: After a level jump in the input level p _E and thus also in the output level p _A , there is a sudden change in the current Ip . If the magnetic amplifier M has a high gain μ, this would result in a large change in heating current if a voltage difference AU did not occur, which counteracts the controlling effect of Jp via the feedback current I% that is set in. The high gain μ appears to be reduced by the factor (1 + μ α) at time t = 0.

Δ I _n (t = 0) =

ί + μα

(5)

The change in heating current causes the thermistor to change its resistance over time according to an exponential function with the time constant T _H (which is relatively large for electrical components). The current Ip then approaches its setpoint again according to the same time function. At the same time, however, the feedback current / ^ according to equation (3) is also brought back to zero by the motor. If the time constant T ₁ . If the feedback is made equal to the thermal thermistor time constant T _n , then by suitable choice of a value a ₀ for the factor α, the heating current I _H no longer changes in the further course of the control process. The control process then runs according to the behavior of the NTC thermistor according to an exponential function with the NTC thermistor time constant T _H. For smaller or larger values of α, a heating current adjustment that is too large or too small is initially carried out, which is then corrected accordingly during the control process. The time constant of the control process is then:

(6)

It is possible to set the time constant of the control and thus also the modulation gain by the factor α as the thermistor allows, while the control gain μ can be made as large as the required residual error requires, regardless of this.

In the exemplary embodiment, an indirectly heated thermistor is used as the actuator. But it is also possible a directly heated thermistor or another current or voltage dependent resistor to use. Instead of the potentiometer, which is used to set the equivalent voltage, a Variable transformer with a downstream rectifier can be driven by the motor.

Claims (4)

Patent claims: 1. Pilot-controlled level control for an electrical communication system with a pilot voltage receiving and rectifying pilot receiver and a downstream DC amplifier acting on an actuator of a controllable attenuator or amplifier in the transmission path, characterized in that an equivalent voltage (Un ') by a motor (Z) in is regulated in the sense that it is equal to the output voltage (U _n ) of the direct current amplifier (M), that the motor is fed by the difference between the two voltages (U # - U _n ) and that the direct current amplifier is additionally supplied with a direct current (I _R ) is supplied, which is proportional to this voltage difference (U _H - U ₁₁ '). 2. Pilot-controlled level control according to claim 1, characterized by a relay (A) which, if the pilot voltage fails, switches the actuator (HL) from the output voltage (U _H ) of the DC amplifier (M) to the equivalent voltage (U ₁₁ ') and the control the backup voltage stops. 3. Pilot-controlled level control according to Claim.2, characterized in that when the pilot voltage is present, the equivalent voltage (U _H ^r ) is loaded with a resistor (R ₂ ) which is equal to the resistance of the actuator (HL) . 4. Pilot-controlled level control according to one of the preceding claims, characterized in that a magnetic amplifier (M) with galvanically separated control windings is used as the direct current amplifier. 1 sheet of drawings © 909 768/291 5.